1. Field of the Invention:
This invention relates generally to digital data processing systems, and in particular, to the architecture of a MOS/LSI microprogrammed computer which is fabricated on a single semiconductor chip.
2. Description of the Prior Art:
An important improvement in computer control implementation is the replacement of conventional transistor logic with "stored logic" or microprogrammed control, stored in a high speed, nondestructive read-only memory (ROM). Microprogramming has made it possible to have the same comprehensive "industry standard" instruction set (operation codes) built into a line of new computers which are architecturally compatible but which may have different internal hardware, organization, and structure. Additional advantages which the microprogramming approach offers is the minimum geometry for circuit logic functions which may be implemented by MOS/LSI circuit techniques.
A general understanding of a digital computer is necessary to understand the objects of the invention. Any data processing system, including a digital computer, can be organized into five distinct functional sections: input, storage, arithmetic and logic unit (ALU), output, and control. These functional sections communicate with each other by means of electronic signals which represent data, instructions, and control signals. The order, timing, and direction in which this information flows within and between the functional sections are effected by the control section. The control section directs the operations of the entire computer. It receives units of information from the storage section which tell it which operations are to be performed and where the data to be operated on are located in the storage section. After the control section determines the exact construction to be executed, it then issues control signals to open and close the specific gates throughout the system, thus permitting the necessary data in the form of electrical signals to flow from one functional unit to another in the execution of that operation. Once the arithmetic and logic section has performed its function, the control section may issue the necessary control instruction to permit the results to be transmitted back into the storage section or to be channeled into some output device to be stored on another storage media. At the end of the execution of an instruction, the control section causes the computer to proceed to fetch and decode the next instruction.
Implementation of microprogrammed control for digital computers has made possible the control of microspect functions (adder, shifter, and other hardware facilities) by means of minimum geometry, extremely low load MOS/LSI logic function elements. It is a general object of the present invention to provide a microprogrammed computer system having improved performance and higher packing density. In particular, it is an object of the invention to provide such a microprogrammed computer which may be implemented by MOS/LSI techniques on a single semiconductor chip.